The electrical condition of hot surfaces. Part VI.—A gold surface catalysing the combustion of carbonic oxide

A study of the electrical condition of hot surfaces in contact with gases has revealed the fact in several important respects a striking parallel exists between such electrical condition and the catalytic properties of the surfaces. Thus, it has been found that, whereas at comparatively low temperatures the specific effect of a surface upon the potential it acquires in contact with a gas is hightly pronounced, with increasing temperature such specificity tends to disappear until, at a sufficiently high temperature, the value of the surface potential is almost wholly determined by the nature of the gas and is nearly independent of the nature of the surface itself. This may be compared with the fact, established by Bone and his co-workers, that the differences between the catalytic powers of various surfaces, which are often considerable at low temperatures, diminish as the temperature is raised, until they practically disappear. Furthermore, it is now well recognized that the catalytic properties of a surface are intimately connected with its structure, and a close parallelism has been observed between the surface potential of a metal and changes in its superficial structure brought about by heat treatment. Finally, it has been found that the electric current which can be drawn from a heated metallic surface in contact with a gas increases rapidly with increasing temperature, an observation which has its parallel in the well-known rapid increase in the catalytic activity of such a surface with increasing temperature. The present investigation was undertaken with the object of determining the relationship, if any, between the role played by moisture in promoting the heterogeneous catalytic combustion of carbonic oxide with oxygen and the structure of the surface as revealed by its catalytic activity and electrical condition.